Magnetic electron multiplier gate



March 11, 1958 w. c. WILEY 2,826,704

MAGNETIC ELECTRON MULTIPLIER GATE Filed Jan. 3, 1955 m 2 Shts-Sheet 1 OSCILLOSCOPE FORMING CIRCUIT POWER SUPPLY JNVENTOR.

Y Y BY WILLI%WILE I AT ORNEY March 11, 1958 Filed Jan. 3, 1955 W C. WILEY FIG- "'2 MAGNETIC ELECTRON IVIULTIPLIER GATE 2 Sheets-Sheet 2 WILLIAM INVENTOR.

C. WILEY TORNEY United States atent O MAGNETIC ELECTRON MULTliPLlER GATE William C. Wiley, Detroit, Mich, assignor to Bendix Aviation Corporation, Detroit, Mich, a corporation of Delaware Application January 3, 1955, Serial No. $79,339

7 Claims. (Cl. 250--2ll7) This invention relates to magnetic electron multipliers and more particularly to a highly efficient gate for use in electron multipliers.

Gates, such as screen type grids, have been used in electron multipliers to control the how of electrons through the gate. Such gates have not been entirely successful because of their inefiiciency in blocking or providing for the passage of electrons in the multiplier. Furthermore, in order to obtain a high degree of control, voltage pulses of relatively great magnitude, such as 260 volts, have to be applied to the gate to open or close the gate. Voltage pulses on the order of 200 volts are relatively difficult to produce without distortion, especially when fast rise and fall times are required, such as in the field of timeof-flight mass spectrometry. Such distortion aiiects the accuracy and efiiciency of the gate.

This invention provides a simple and highly efficient gate for use in a magnetic electron multiplier. The gate includes first and second plates disposed between a pair of plates in a multiplier so that the electrons emitted. by the preceding plate are received in the region between the first and second plates. The first and second plates are normally biased to provide a substantially field-free region between the plates for blocking the passage of electrons through the region. Upon the application of a voltage pulse of moderate magnitude to one of the plates, the electric field produced in the region between the plates acts to pass electrons through the region.

Y An object of this invention is to provide a gate for con trolling the passage of electrons through the gate.

Another object of this invention is to provide a gate for use in a magnetic electron multiplier to control the passage of electrons through the gate at any instant.

. A further object is to provide a gate of the above character which includes first and second plates for blocking the passage of any electrons through the region between a.

the plates upon a normal biasing of the plates and for passing electrons through the region upon the application of a Voltage pulse of moderate magnitude to one of the plates to provide an electric field between the plates.

Still another object is to provide a gate of the above 3 character which is simple in construction and highly etficient and reliable in its operation.

Other objects and advantages will be apparent from a detailed description of the invention and from the ap pended drawings and claims.

In the drawings:

Figure 1 is a schematic view, partly in block form and partly in perspective, of an electron multiplier including a gate constituting one embodiment of this invention.

Figures 2 and 3 are plan views schematically illustrating the operation of the electron multiplier and gate shown in Figure 1 under diiierent voltage relationships in the multiplier.

In one embodiment of the invention a source it), such as an ion source for a mass spectrometer, is adapted to emit a stream of particles. The source may emit either uncharged particles such as neutrons or charged particles 2,8261% Patented Mar. 11, 1958 lCQ such as ions. The source it is adapted to emit particles towards a window 12 in an electrode 14 having a relatively large lateral dimension. The window 12 is disposed in direct alignment with a plate 16 so that the particles from the source lll will pass through the window and will impinge upon the plate.

The plate 16 forms part of an electron multiplier generally indicated at 13 which also includes plates 2d, 22, 2d, 26 and 28. Each of the plates is made from a suitable material to secondarily emit electrons when electrons or other particles strike the plates. For example, the plates may be made from a beryllium copper alloy having ap-. proximately 2% by weight of beryllium. The plates are positioned in laterally contiguous relationship to one another and because of the angle of disposition of the electrode 14, the plates are positioned at different distances from the electrode. An anode 3d is positioned in substantially perpendicular relationship to the plate 28 to receive electrons emitted by the plate.

Plates 32 and 34 are disposed in substantially parallel relationship to each other and in substantially perpendicular relationship to the plates 22 and 24. The plates 32. and 34- are so disposed between the plates 22 and 24 that electrons emitted by the plate 22 are received at an intermediate position in the region between the plates. The plates 32 and 34 are placed a relatively small distance apart, such as 1 millimeter. Plates 33 and 35 are dis posed between the plates 2-2 and 24- in the electron multiplier and are separated from each other a relatively small distance, such as l millimeter, so that the electrons emitted by the plate 22 will pass between the plates and enter the region between the plates 32 and In the embodiment shown, the plates 32 and 3d are of planar configuration and are disposed in perpendicular relationship to the plates in the multiplier for convenience only. Actually, the plates 32 and 34 may be of curved configuration and may be disposed, relative to the plates in the multiplier, in any position suitable for receiving electrons in the region between the plates.

An anode 36 is positioned in substantially perpendicular relationship to the plates 32 and 3 2 and is disposed to receive any electrons flowing through the region between the plates. The anode 36 is connected to ground through a resistance 33 and is also connected to an indicator, such as an oscilloscope ill, for providing an indication of the electrons impinging upon the electrode Direct voltages are applied to the plates 16, 2d, Z2, Z4, 26 and 23 to produce a substantially constant electric field between the electrode lid and the plates. Since the plates 16, 20, 22, 24, as and 28 are positioned at different distances from the electrode it, different voltages are applied to the plates to produce the substantially constant electrical field. The voltages are applied to the plates from a power supply 52. For example, voltages of approximately 500, 300, l00, +50, +250 and +450 may he applied to the plates M, iii), 22, 24, 2-6 and 28, respectively. A direct voltage, such as +1200 volts is also applied to the electrode 14 and the anode as from the power supply 42.

Direct voltages of substantially the same magnitude are applied to the plate 32 from the power supply 42 and to the plate 34 from the power supply through a resistance 44 to produce a substantially field-free region between the plates. For example, approximately volts may be applied to the plates 32 and 34. Actually, the plate 34 may be biased at approximately volts to make the plate slightly more negative than the plate 34 and to produce a slight electric field between the plates. Direct voltages are also applied to the plates 33 and from the power supply 42. For example, voltages of approximately -l5 and +15 may be applied to the plates 53 and 35, respectively.

The plate 34 is connected to a pulse forming circuit 46 through a coupling capacitance 47. The pulse forming circuit 46 is adapted to introduce positive pulses of voltage to the plate 34 at particular times. For example, Model 903 of a pulse generator manufactured by Berkeley Scientific Instrument Company of Richmond, California, may be used to produce positive voltage pulses at desired times. The pulse forming circuit disclosed in co-pending application Serial No. 288,104 filed May 16, 1952, by Macon H. Miller and William C. Wiley may also be conveniently adapted for use.

A magnetic field, as well as an electric field, is provided between the electrode 14 and the plates 16, 2t), 22, 24, 26 and 28, and is also provided in the region between the plates 32 and 34. The magnetic field is produced in a vertical direction substantially parallel to the faces of the plates by a pair of pole pieces 48, one positioned above the plates and the other positioned below the plates. For example, a magnetic field of 35 gauss may be provided by the pole pieces 48.

The particles produced by the source it? travel through the Window 12 in the electrode 14 and impinge upon the plate 16. Because of the particular material from which the plate 16 is made, the plate emits electrons when the particles from the source Iii) impinge upon it. The number of electrons emitted by the plate 16 is dependent, among other factors, upon the number of particles impinging upon the plate.

The electrons emitted by the plate 16 are subjected to the combined action of the electrical field between the electrode 14 and the plate and the magnetic field between the pole pieces 48. This causes the electrons to travel in a curved path indicated in broken lines at th in Figure 2 and mathematically defined as a cycloid. As a result of their cycloidal movement, the electrons emitted by the plate 16 impinge upon the plate 20 and cause 'a proportionately increased number of electrons to be emitted by the plate Zil.

In like manner, the electrons emitted by the plate 20 travel in a cycloidal path to the plate 22 which upon receiving the electrons emits a proportionately increased number of electrons which in turn travel in a cycloidal path to the region between the plates 32 and 34. Because of the substantially field-free region provided between the plates 32 and 34 and because of the magnetic field disposed in the region, any electrons introduced to the region from the plate 22 are prevented from passing through the region. This causes the electrons to continue their travel in a cycloidal path to the plate 24 which emits a proportionately increased number of electrons for travel in a cycloidal path to the plate 26. The plate 26 in turn emits a proportionately increased number of electrons which are received by the plate 28 and the electrons emitted by the plate 28 are collected by the anode 30. The

path of electron flow when the plates 32 and 34 are biased at their normal value is illustrated by the broken lines in Figure 2 of the drawings.

When a relatively small voltage pulse is applied to the plate 34 from the pulse forming circuit 46, such as a voltage pulse having a magnitude of volts, an electric field having a particular strength is produced between the plates during the application of the pulse. Since the plate 34 is more positive than the plate 32 during this period, any electrons introduced to the region between the plates are initially attracted towards the plate 34. However, because of the magnetic field in the region, the electrons flow through the region in successive cycloidal paths illustrated at 52 (Figure 3) and impinge upon the anode 36. The oscilloscope provides an indication of the electrons impinging upon the anode 36. The electric field produced in the region is of a magnitude to produce a movement of the electrons through the region in small cycloidal paths so that the electrons will not strike the plates.

- In actual laboratory tests that have been conducted,

substantially no electrons passed through the region between the plates 32 and 34 during a normal biasing of the plates. Upon the application of a voltage pulse of moderate magnitude to the plate 34, electrons emitted by the plate 22 are passed through the region. In this way, the plates 32 and 34 act as a gate to control the flow of ions through the region between the plates. The gating action provided by the plates has been found to be much more efiective than any gate heretofore used in magnetic electron multipliers.

A pulse may be applied to the plate 34 at a particular time when electrons produced by certain groups of particles from the source 10 are expected to arrive at the region between the plates 32 and 34. This produces a passage of the electrons through the region between the plates 32 and 34 and the oscilloscope provides information which is indicative of the number of particles in the group from the source 10.

The invention disclosed above has several advantages. The gate including the plates 32 and 34 is very simple to construct and is reliable in its operation. By provid ing a substantially field-free region between the plates, substantially all of the electrons introduced to the region are blocked from passage through the region. However, upon the imposition of a voltage pulse of moderate magnitude to the plate 34 to produce an electric field between the plates, substantially all of the electrons introduced to the region pass through it to the anode 36. This provides a gate which has a high gain characteristic and which is highly etficient in its operation.

Although this invention has been disclosed and illustrated with reference to a particular application, the principles involved are susceptible of numerous other applications which will be apparent to persons skilled in the art. The invention is, therefore, to be limited only as indicated by the scope of the appended claims.

I claim:

1. In combination with a magnetic electron multiplier, first and second plates disposed to provide between them a first region for receiving electrons emitted by a plate in the multiplier, means for biasing the first and second plates to maintain the first region substantially field-free to block from passage through the region any electrons emitted by the plate in the multiplier, and means for imposing a voltage pulse upon the second plate to produce an electric field in the first region for passing through the region electrons emitted by the plate in the multiplier.

2. In combination with a magnetic electron multiplier, first and second plates disposed between a pair of plates in the multiplier, the first and second plates being disposed to provide between them a first region for receiving electrons emitted by the preceding plate in the pair, means for normally maintaining the first region substantially free of any field to prevent the passage of electrons through the region and to produce a movement of the electrons to the succeeding plate in the pair, and means for producing an electric field in the first region to produce a movement of electrons through the region.

3. A gate in a magnetic electron multiplier, including, first and second plates disposed in substantially parallel relationship to each other to provide between them a first region of restricted width for receiving electrons emitted by a plate in the multiplier, means for imposing substantially equal voltages upon the first and second plates to maintain the first region substantially field-free to prevent a movement through the region of any electrons emitted by the plate in the multiplier, and a circuit for introducing a voltage pulse of moderate magnitude to the second plate to produce an electric field in the first region for passing through the region electrons emitted by the plate in the multiplier during the application of the voltage pulse.

4. In combination with a magnetic electron multiplier, first and second plates disposed between a pair of plates in the multiplier, the first and second plates being disposed to receive in the region between them electrons emitted by the preceding plate in the pair, means for normally biasing the first and second plates relative to each other to prevent the passage of any electrons through the region between the plates and to provide for the movement of the electrons to the succeeding plate in the pair, and means for imposing a voltage pulse on the second plate relative to the first plate for producing an electrical field between the plates to provide for the passage through the region between the plates of electrons received in the region during the application of the pulse.

5. In combination with a magnetic electron multiplier, a first plate disposed between a pair of plates in the multiplier in substantially perpendicular relationship to the plates, 2. second plate disposed between the pair of plates in the multiplier in substantially perpendicular relationship to the plates and spaced from the first plate to provide a first region between the first and second plates for receiving electrons emitted by the preceding plate in the multiplier, means for providing a substantially field-free region between the first and second plates to block the passage of electrons through the first region and to provide for a movement of the blocked electrons to the succeeding plate in the pair, means for imposing an electric field between the first and second plates to produce a movement of electrons through the first region and to prevent their movement to the succeeding plate in the multiplier, and means disposed at the end of the first region to collect the ions passing through the region.

6. In combination with a magnetic electron multiplier, first and second plates disposed to provide a first region between them, the first region being disposed to receive electrons emitted by a plate in the multiplier, means for providing a magnetic field in the first region, means for maintaining the first region substantially free of any electric field to block from passage through the region any electrons emitted by the plate in the multiplier, and means for imposing an electric field in the first region to produce a movement of electrons through the region in successive cycloidal paths.

7. In combination with a magnetic electron multiplier, first and second plates disposed to receive in the region between them electrons emitted by a plate in the multiplier, means for providing a magnetic field in the region between the first and second plates, means for imposing substantially equal voltages upon the first and second plates to maintain the region between them substantially free of any electric field to block the passage of any electrons through the region, and means for applying a voltage pulse of moderate magnitude to the second plate to produce an electric field in the region for passing electrons through the region in successive cycloidal paths, the electric field being of a magnitude to maintain the movement of the electrons through the region in small cycloidal paths so that the electrons will not strike the plates.

References Cited in the file of this patent UNITED STATES PATENTS 2,147,756 Ruska Feb. 21, 1939 2,179,112 Barthelemy Nov. 7, 1939 2,207,355 Shockley July 9, 1940 2,245,624 Teal June 17, 1941 2,563,807 Alfven et al. Aug. 14, 1951 

